Conventionally, there are known gas detectors of the type using a TDLAS (tunable diode laser absorption spectroscopy) scheme in which laser beam matched an absorption line wavelength of a detection target gas (such as a methane gas or alcoholic gas) is radiated into a detection space by using an absorption line peculiar to a gas. Then, the presence or absence, the concentration, and the like of the detection gas are detected by measuring the attenuated state of the radiated laser beam.
As semiconductor laser devices to be used with gas detectors of the above-described type, there are known tunable semiconductor lasers, such as a DFB (distributed feedback) laser disclosed in Patent Document 1 as described latter and a DBR (distributed Bragg reflector) laser disclosed in Patent Document 2 as described latter.
As shown in FIG. 9, the DFB laser, which is disclosed in Patent Document 1, is constructed such that, for example, an active layer 51 and an InP layer 52 are formed above a one-surface side of an n-InP substrate 53, and an n-type electrode 54 is formed on an opposite surface side of the n-InP substrate 53.
A SiO2 insulation film 55 including a window and a p-type electrode 56 formed to contain Au for drive current injection are formed above the active layer 51.
Further, electrodes 59a and 59b for a resistive film 58 are formed respectively as islands in the right hand region of the p-type electrode 56.
Further, the resistive film 58 including a SiO2 insulation film 57 and Pt is formed above the active layer 51.
In this case, two ends of the resistive film 58 are formed in contact with the electrodes 59a and 59b previously formed.
As shown in FIGS. 10A and 10B, the DBR laser, which is disclosed in Patent Document 2, includes a semiconductor optical device 64 and a heatsink 65, in which the semiconductor optical device 64 includes an optical waveguide 62 and a heating portion 63 formed via an insulation film 67 to heat at least one part of the optical waveguide 62; and the heatsink 65 is formed to mount the semiconductor optical device 64, to be in direct contact with the one part of the optical waveguide 62, and to be in contact with other parts of the optical waveguide 62 through a space portion 66.
In addition, a substrate 70 is periodically etched, and a corrugation-shaped diffraction grating 69 is thereby formed in a region 80 other than an active region 61 of the optical waveguide 62.
According to the DBR laser, among the regions other than the active region 61, a portion where the diffraction grating 69 is formed is referred to as a DBR region C, and the remaining portion is referred to as a phase control region B.
As shown in FIG. 10B, an InGaAsP guide layer to be used as a non-radiation region 80, and an InP cladding layer 71 are formed in the peripheral portion of the active region 61.
An n-type electrode 68 is formed on the upper surface of the active region 61 via the InP cladding layer 71 by performing vapor deposition of, for example, Au and Ge.
A p-type electrode (not shown) is formed on the bottom surface of the substrate 70 by performing vapor deposition of, for example, Au and Zn.
As DFB lasers having a configuration different from that of the DFB laser disclosed in Patent Document 1 as described above are, for example, a partial diffraction grating semiconductor laser (PC-LD) disclosed in Patent Document 3 as described latter; and a distributed feedback semiconductor laser having two diffraction gratings, which laser is disclosed in Patent Document 4 as described latter.
Patent Document 1: Jpn. Pat. Appln. KOKAI Publication No. 4-72783
Patent Document 2: Jpn. Pat. Appln. KOKAI Publication No. 9-74250
Patent Document 3: Jpn. Pat. Appln. KOKAI Publication No. 6-310806
Patent Document 4: Jpn. Pat. Appln. KOKAI Publication No. 2004-31827